586 research outputs found
Inertial and dimensional effects on the instability of a thin film
We consider here the effects of inertia on the instability of a flat liquid
film under the effects of capillary and intermolecular forces (van der Waals
interaction). Firstly, we perform the linear stability analysis within the long
wave approximation, which shows that the inclusion of inertia does not produce
new regions of instability other than the one previously known from the usual
lubrication case. The wavelength, , corresponding to he maximum
growth, , and the critical (marginal) wavelength do not change at
all. The most affected feature of the instability under an increase of the
Laplace number is the noticeable decrease of the growth rates of the unstable
modes. In order to put in evidence the effects of the bidimensional aspects of
the flow (neglected in the long wave approximation), we also calculate the
dispersion relation of the instability from the linearized version of the
complete Navier-Stokes (N-S) equation. Unlike the long wave approximation, the
bidimensional model shows that can vary significantly with inertia
when the aspect ratio of the film is not sufficiently small. We also perform
numerical simulations of the nonlinear N-S equations and analyze to which
extent the linear predictions can be applied depending on both the amount of
inertia involved and the aspect ratio of the film
Application du système d'acquisition de données Plurimat 20 en physique
Deux applications du système d'acquisition de données Plurimat 20 sont présentées. L'une concerne un appareil destiné à l'enregistrement automatique sur minicassette de 48 paramètres indépendants, quasi simultanément, provenant de mesures de grandeurs physiques (telles que des températures) codées en fréquence. L'échantillonnage des paramètres et le couplage de la minicassette au Plurimat 20 sont décrits. L'autre application a trait à l'acquisition d'événements corrélés en Physique Nucléaire ; une expérience de corrélation angulaire α-γ, par la réaction 18O(t, αγ) 17N, est décrite dans sa partie technique
Hitch-hiking effect and linkage disequilibrium: the example of two closely linked loci in the pig, Halothane Sensitivity (HAL) and Phosphohexose Isomerase (PHI)
International audienc
Relative contributions of solid skeleton visco-plasticity and water viscosity to the poro-mechanics behavior of callovo-oxfordian claystone
The Callovo-Oxfordian claystone is a saturated porous medium. Its transfer properties, including its low permeability [16] make it an interesting candidate for underground radioactive waste disposal.
The drained tests performed on the claystone, collected by ANDRA1 from samples at 500 meters depth [16, 9], exhibits a damageable visco-elasto-plastic behavior. This viscous behavior includes both the viscosity of the skeleton and the water. In existing models [5, 6, 11, 1], the creep phenomena are attributed either to the water permeability, to the skeleton visco-plasticity or sometimes both [13].
In a first step, a simplified analysis is proposed to understand the contribution of each phenomenon with respect to the consolidation time. This study indicates that the apparent characteristic time is the sum of those related to the skeleton and water permeability.
To handle both non-linear and viscous phenomena, the damage law [15], coupled with the basic creep model [14] is used to characterize the solid skeleton of the claystone. The fluid behavior is integrated with the poro-mechanical model [7] implemented in the finite element code CAST3M [4]. The proposed model (visco-elastic damageable skeleton + saturating fluid) is used to simulate an excavation from the ANDRA underground laboratory (located in Bure–France).
This application allows the understanding of how both viscous phenomena combine at each step of the calculation. Just after the excavation, water overpressure decreases near the gallery approaching zero due to the damage and then increases the permeability. The viscosity is then controlled by the solid skeleton creep rates. Later, the redistribution of hydraulic pressure is of more importance and permeability again plays a major role
Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy
The disordered potential landscape in an InGaAs/InAlAs two-dimensional
electron gas patterned into narrow wires is investigated by means of scanning
gate microscopy. It is found that scanning a negatively charged tip above
particular sites of the wires produces conductance oscillations that are
periodic in the tip voltage. These oscillations take the shape of concentric
circles whose number and diameter increase for more negative tip voltages until
full depletion occurs in the probed region. These observations cannot be
explained by charging events in material traps, but are consistent with Coulomb
blockade in quantum dots forming when the potential fluctuations are raised
locally at the Fermi level by the gating action of the tip. This interpretation
is supported by simple electrostatic simulations in the case of a disorder
potential induced by ionized dopants. This work represents a local
investigation of the mechanisms responsible for the disorder-induced
metal-to-insulator transition observed in macroscopic two-dimensional electron
systems at low enough density
Local Density of States in Mesoscopic Samples from Scanning Gate Microscopy
We study the relationship between the local density of states (LDOS) and the
conductance variation in scanning-gate-microscopy experiments on
mesoscopic structures as a charged tip scans above the sample surface. We
present an analytical model showing that in the linear-response regime the
conductance shift is proportional to the Hilbert transform of the
LDOS and hence a generalized Kramers-Kronig relation holds between LDOS and
. We analyze the physical conditions for the validity of this
relationship both for one-dimensional and two-dimensional systems when several
channels contribute to the transport. We focus on realistic Aharonov-Bohm rings
including a random distribution of impurities and analyze the LDOS-
correspondence by means of exact numerical simulations, when localized states
or semi-classical orbits characterize the wavefunction of the system.Comment: 8 pages, 8 figure
Scanning Gate Spectroscopy of transport across a Quantum Hall Nano-Island
We explore transport across an ultra-small Quantum Hall Island (QHI) formed
by closed quan- tum Hall edge states and connected to propagating edge channels
through tunnel barriers. Scanning gate microscopy and scanning gate
spectroscopy are used to first localize and then study a single QHI near a
quantum point contact. The presence of Coulomb diamonds in the spectroscopy
con- firms that Coulomb blockade governs transport across the QHI. Varying the
microscope tip bias as well as current bias across the device, we uncover the
QHI discrete energy spectrum arising from electronic confinement and we extract
estimates of the gradient of the confining potential and of the edge state
velocity.Comment: 13 pages, 3 figure
Imaging Electron Wave Functions Inside Open Quantum Rings
Combining Scanning Gate Microscopy (SGM) experiments and simulations, we
demonstrate low temperature imaging of electron probability density
in embedded mesoscopic quantum rings (QRs). The tip-induced
conductance modulations share the same temperature dependence as the
Aharonov-Bohm effect, indicating that they originate from electron wavefunction
interferences. Simulations of both and SGM conductance maps
reproduce the main experimental observations and link fringes in SGM images to
.Comment: new titl
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